Nuclear safety officials in France said they were “pessimistic” about whether engineers could prevent a meltdown at the Fukushima power plant after a pool containing spent fuel rods overheated and boiled dry. Last night radiation levels were “extremely high” in the stricken building, which was breached by an earlier explosion, meaning radiation could now escape into the atmosphere.

As Japan resorted to increasingly desperate measures – including dumping water on the site from helicopters – there were accusations that the situation was now “out of control”.

The EU urged member states to check Japanese food imports for radioactivity.

As the exodus of people living near the plant continued, the governor of the Fukushima region, Yuhei Sato, hit out at the government, saying the “anxiety and anger” of residents had “reached a boiling point”.

Japan’s Emperor Akihito made a rare address to the nation urging the Japanese to pull together, but hinted at his own fears for the nuclear crisis by saying: “I hope things will not get worse.”

The official death toll from last Friday’s earthquake and tsunami now stands at 4,314, with another 8,606 listed as missing.

Thousands of people who are still waiting for food aid in the remotest areas of the disaster zone endured fresh misery yesterday as heavy snow began to fall across northern Japan.

But all eyes were on the Fukushima Daiichi nuclear plant as the Japanese authorities admitted to concerns over rising temperatures in three pools containing spent fuel rods.

A failure of the cooling system, which has crippled the entire plant, meant water in the No 4 pool started to boil.

If the water evaporates and exposes the rods, a meltdown could occur, and last night the US Nuclear Regulatory Commission (USNRC) said there was no water left in the pool, resulting in “extremely high” radiation levels.

An earlier fire and explosion in the No 4 reactor building is thought to have breached the protective walls around the pool, meaning radiation could escape into the atmosphere.

Attempts to cool the site by dumping seawater from helicopters had to be aborted at one stage because of dangerous radiation levels in the air above the plant.

A police water cannon was brought in to help blast water into the overheating reactors and pools, but there were dire warnings that it may be too late to prevent a disaster.

Thierry Charles, a safety official at France’s Institute for Radiological Protection and Nuclear Safety (IRSN) said:

“The next 48 hours will be decisive. I am pessimistic, because since Sunday I have seen that almost none of the solutions has worked.”

Asked about the maximum possible amount of radioactive release, he said “it would be in the same range as Chernobyl”.

Francois Baroin, a French government spokesman, went even further, saying: “In the worst of cases, it could have an impact worse than Chernobyl.”

Control

He added: “Let’s not beat about the bush. They have visibly lost the essential of control. That is our analysis, it’s not what they are saying.”

France’s ecology minister Nathalie Kosciusko-Morizet, had earlier said that “the worst scenario is possible and even probable”.

The fuel rod pools contain spent uranium rods which remain extremely radioactive after being used in the reactor, and have to be constantly cooled until safe for disposal.

Guenther Oettinger, the EU energy commissioner who warned of a potential “apocalypse” on Tuesday, said: “The French government has advised its citizens to leave Japan. This should be the advice to other people there too.”